Roman Calculator

CodersDojoSweden , running in Linköping, was
looking for a new Kata which was sufficiently simple to get beginners up
and running. ThomasNilsson suggested a
calculator using Roman numerals.

Problem Description

“As a Roman Bookkeeper I want to add Roman numbers because doing it
manually is too tedious.” Given the Roman numerals, (IVXLCDM which means
one, five, ten, fifty, hundred, fivehundred and a thousand
respectively), create two numbers and add them. As we are in Rome there
is no such thing as decimals or int, we need to do this with the
strings. An example would be “XIV” + “LX” = “LXXIV”

There are some rules to a Roman number:

Numerals can be concatenated to form a larger numeral (“XX” + “II”
= “XXII”)

If a lesser numeral is put before a bigger it means subtraction of
the lesser from the bigger (“IV” means four, “CM” means ninehundred)

If the numeral is I, X or C you can’t have more than three (“II” +
“II” = “IV”)

If the numeral is V, L or D you can’t have more than one (“D” + “D”
= “M”)

Clues

String grouping and concatenation is key to solving this kata. But
remember the rule that lesser numerals can preceede bigger ones.

Suggested Test Cases

The first test case(s) are pretty easy. I won’t put the test cases here
since I feel this kata is one of the better ones I have done when it
comes to practicing finding out what the next test case is.

Comments from those who are working on this Kata

When I invented it I did not know how well it would work. I was
pleasantly surprised to see it work out to be a kata very focused on
finding test cases. – ThomasNilsson

This kata does not immediately show the “behaviour” aspect as does e.g.
the Bowling kata. By this I mean the behaviour of a class under test, as
opposed to testdriving a single method. However, in the Linköping dojo,
we decided on adding this aspect by changing the story to “As a Polish
born Roman Accountant…” and thereby introducing the Polish reverse
notation to the calculation. The first test would then become:

And we also decided to add this aspect on an already running partial
solution in the middle of the kata. This creates the situation of
refactoring the API into another structure. We’ll see how this turns
out. – ThomasNilsson